The present invention relates to a method and apparatus for increasing the thrust applied to coiled tubing over that applied by its injector alone during its injection into and withdrawal from a well bore. The apparatus of the invention is mounted in series with an injector and is used in situations where additional thrusting force is required to cause the tubing in the well bore to overcome high resisting forces due to obstructions, the annulus being sanded up, or the like. The apparatus provides a short, repeatable reciprocating stroke in either direction.
Devices and methods for injecting coiled tubing into and retrieving it from wells are well known. Prior art injection systems include U.S. Pat. Nos. 6,142,406; 5,842,530; 5,839,514; 5,553,668; 5,309,990; 5,244,046; 5,234,053; 5,188,174; 5,094,340; 4,899,823; 4,673,035; 4,655,291; 4,585,061; and many other similar disclosures. In the prior art an injector at the wellhead is used to grip and control the injection and withdrawal of the tubing.
Conventional track injectors utilize gripper blocks mounted on two continuous parallel and opposed conveyor chains which are urged or pushed against the outer surface of the tubing. The interface forces between the gripper blocks and the tubing permit developing frictional forces which are used to transfer tangential loads from the conveyor chains to the tubing and vice versa. If insufficient interface force is applied to the tubing by the gripper blocks, slippage with attendant loss of control and wear occurs between the blocks and tubing. If excessive interface force is applied to the tubing by the gripper blocks, the tubing wall may be distorted and damaged or the injector may be damaged. A problem with such tracks results when the track is rotated into or out of engagement with the tubing from the sprockets at the ends of the track mounting assembly. This rotation can cause differential movement between the track and the tubing in the direction of the tubing axis so that rubbing occurs. This rubbing will cause undesirable wear of both the tubing and the gripper blocks.
Historically, the approach used to increase the injection forces with conventional track injectors has been to lengthen the injector while maintaining a sufficiently safe interface force between the individual gripper blocks and the tubing. U.S. Pat. No. 5,842,530 for example shows provision of substantially more gripper blocks along the length of its injector.
Other injectors utilizing two continuous, parallel, and opposing track injectors having grooved shoes or blocks mounted thereon are known in the art. These opposing track units have facing portions where the multiplicity of gripping blocks run parallel for gripping the tubing therebetween and are typically positioned in line, directly adjacent and above the wellhead.
Another approach has been to utilize a large diameter driven wheel with an annularly is grooved outer diameter to conform to and support the tubing. Relatively small-diameter hold-down idler rollers radially press the tubing against the wheel to provide extra interface force between the tubing and the wheel so that high tangential frictional forces can be imparted to the tubing by the wheel without maintaining large back tensions. These hold-down rollers have arcuate faces to match the tubing. One such wheel type injector is disclosed in U.S. Pat. No. 5,839,514.
A more recent injector system known in the art is a linear injector, which pulls on only one side of the tubing. For this type of device, coiled tubing is driven along a single linear section of an endless chain conveyor with normal forces being applied by an opposing linear array of small-diameter arcuate face hold-down idler rollers. These hold-down rollers are sized to conform to the tubing. Such a linear or one-track injector eliminates the necessity of synchronizing the two opposed sides of a conventional track type injector and is less damaging to the surface of the coiled tubing, but it requires a much longer unit, which of necessity extends much higher and requires additional overhead clearance. Additionally, such an injector is more expensive because it requires a considerable number of gripper blocks and rollers and a longer support track.
Copending U.S. Provisional Patent Application xe2x80x9cCoiled Tubing Injector Utilizing Opposed Drive Modules and Having an Integral Benderxe2x80x9d, Ser. No. 60/304,681, filed Jul. 11, 2001, utilizes a novel approach to imparting tangential injection forces to the tubing. That invention provides support over a larger portion of the tubing circumference by positioning the driving means around the circumference of the tubing. By using a plurality of sets of opposed individually driven annularly grooved rollers which closely conform to the tubing and alternating the orientations of adjacent roller sets so that they are 90xc2x0 apart about the through axis of the injector, excellent tubing support is provided. That invention is economical and efficient, as well as being lightweight, compact, easy to service and adapt for different tubing sizes.
A major problem with tubing injectors of all types is providing sufficient injection force on the tubing so that not only normal, smoothly operating injection loads are provided, but also sufficient injection force is available to overcome temporary, abnormally high resistances to tubing movement. Such abnormally high loads normally would be the result of a buildup of sand around the tubing, hanging up on a shoulder within the well, or other similar unexpected problems. Generally, such abnormally high loads only occur over a short section of a given well bore, if at all. The conventional means for overcoming such abnormally high injection forces is to use an injector which is able to provide the maximum push/pull required. Generally, the result of such an approach is that the injector is oversized for conventional non-problematic operation. Resulting in an injector that is larger, heavier, and more expensive to build and operate than is necessary for routine operations.
There exist a need for a simple and efficient method to provide an injection force in excess of that required for routine, non-problematic operation without having to provide an injector built to supply the maximum force predicted to be needed in the field.
The present invention utilizes a novel means and method for improving the system of injecting of coiled tubing into and from a well by providing a secondary injection device for supplementing the primary injector means. The secondary injection device is used to increase the axial forces in the tubing over the force provided by the primary injector alone. The selectably operable thrust enhancement device of this invention provides a short, repeatable stroke in either direction. The thrust enhancement device operates by gripping the tubing with a reciprocably moveable means in a first position, moving the moveable means to a second position thereby moving the tubing, then gripping the tubing with a static means at its new position, releasing the tubing from the moveable means, and returning the moveable means to its first position. When the thrust enhancement device is not needed for the injection operation, it is disengaged from the tubing.
One aspect of the invention is a coiled tubing injection system for moving coiled tubing into or out of a wellbore comprising a coiled tubing injector; a static tubing gripper having a closed and an open position; and a moveable tubing gripper having a closed and an open position, said movable tubing gripper being coaxially reciprocable between a first and a second position; wherein the coiled tubing injector, the static tubing gripper and the moveable tubing gripper are positioned coaxially along a length of coiled tubing and are independently selectively operable.
Another aspect of the invention is a coiled tubing injection system for moving coiled tubing into or out of a wellbore comprising a coiled tubing injector; a tubular body having a static transverse deck and a moveable transverse deck with the moveable transverse deck is coaxially reciprocable between a first and a second position; a first tubing gripper attached to the static transverse deck and a second tubing gripper attached to the moveable transverse deck. The first tubing gripper has a first and a second side, each having a back end, a central portion and a front end. The first and second sides are connected at the back ends and have a circularly arcuate groove in the central portion, where the interior surface of the groove serves as a tubing gripping surface when the first tubing gripper is in a closed position. When the first tubing gripper is in an open position the front ends of the first and second sides are separated and when it is in a closed position the front ends of the first and second sides are urged together. Similarly, the second tubing gripper has a first and a second side, each side having a back end, a central portion and a front end. The first and second sides are connected together on the back ends and have a circularly arcuate groove in the central portion, where an interior surface of the groove serves as a tubing gripping surface when the second tubing gripper is in a closed position. The second tubing gripper is in an open position when the front ends of the first and second sides are separated and in a closed position when the front ends of the first and second sides are urged together. The second tubing gripper reciprocates between a first location and a second location in tandem with the reciprocation of said moveable transverse deck between the first position and second position. The coiled tubing injector, the opening and closing of the first tubing gripper, the opening and closing of the second tubing gripper and the reciprocation of the moveable transverse deck are independently selectively operable.
Yet another aspect of the invention is a method for moving coiled tubing into or out of a wellbore using a coiled tubing injector and a thrust enhancer where the thrust enhancer comprises: (i) a tubular body having a static transverse deck and a moveable transverse deck, with the moveable transverse deck coaxially reciprocable between a first and a second position within the tubular body; (ii) a first tubing gripper attached to the static transverse deck, the first tubing gripper having a closed and an open position and an interior surface that serves as a tubing gripping surface when the first tubing gripper is in a closed position; and (iii) a second tubing gripper attached to the moveable transverse deck and reciprocating in tandem with the moveable transverse deck, where the second tubing gripper has a closed and an open position and an interior surface that serves as a tubing gripping surface when the second tubing gripper is in a closed position. The method comprising the steps of: (1) coaxially attaching the thrust enhancer to the coiled tubing injector, (b) feeding a coiled tubing through the functional path of the coiled tubing injector and the first and second tubing grippers; (c) engaging the coiled tubing injector to move tubing into or out of a wellbore; (d) closing the second tubing gripper so that its interior surface will grasp the surface of the coiled tubing; (e) moving the moveable transverse deck from the first position to the second position; (f) closing the first tubing gripper such that it grasps the surface of the coiled tubing; (g) disengaging the second tubing gripper; and (h) moving the moveable transverse deck from the second position back to its first position. Thus, the thrust applied to the coiled tubing is greater than the thrust applied by the coiled tubing injector or the thrust enhancer alone.